Tammy Lessick loved her job as a bookkeeper. But when her son, Dean, was diagnosed with autism, she decided to quit work to take care of him.

"Between all his doctor's appointments and the time I would have to take off when he was sick, it just wasn't working," said Lessick, who lives in Sanford, N.C., with her husband and two children. "It was difficult, but my husband and I decided that we needed to do what was best for our son."

Between Lessick's lost earnings and Dean's special needs, the family struggles to make ends meet.

"There are times when we get frustrated and kind of sad," Lessick said, her voice shaking. "The beginning of the year is easier on us because of the tax money we get back. But by midyear, we're resorting to using credit cards just to buy groceries. Towards the end of the year, we find ourselves having trouble getting food in the house."

It's a common predicament for mothers of autistic children, who earn 56 percent less on average than the mothers of children with no health limitations. They're also 6 percent less likely to be employed, according to a study published today in the journal Pediatrics.

"They have to be advocate, lawyer and case manager for their children," said study author Dr. David Mandell, associate director of the Center for Autism Research at Children's Hospital of Philadelphia. "They learn early on you don't get what your kids need, you get what you negotiate. Those time commitments result in parents -- usually mothers -- saying they just can't manage a job, too."

The income cut compounds the economic burden of autism, a condition already fraught with out-of-pocket costs.

"There's a lot of debate about the cost of treating autism and who should pay," Mandell said. "We really wanted to show the cost of not treating autism, what happens to families when kids are not getting the care they need."

The study also found that mothers of children with autism earn 35 percent less -- $7,189 on average -- than parents of children with another health limitation.

"I don't think there's anything more challenging per se than the health needs of a child with autism compared to those of a child with cystic fibrosis or cerebral palsy," Mandell said. "I think what's different is the system of care. There's a level of fragmentation for autism services, which means a lot of finger pointing about whose paying."

Autism services are hard to come by where Lessick lives, for instance.

"It's very isolating taking care of a special needs child, especially a child with autism, in a small town," she said. "There's not a lot of support out there, not a lot of families in the community that you can try to connect with. In a big city, there might be more options. But not here."

Lessick said she doesn't regret her decision to stay home and care for Dean, who is now 13, but she does miss working.

"I miss interacting with adults. I miss being able to contribute the way I used to," she said. "I used to work all the time, used to support myself all the time. When you go from doing that to not, it's tough."

Many mothers of children with autism, including Lessick, are well-educated, Mandell said.